The present invention relates to an automatic control device for the cleaning power of a vacuum cleaner.
A known device of this type (DE-PS 31 17 507) comprises a vacuum switch arranged in the vacuum area of the vacuum cleaner and designed in such a manner that at least two different negative pressures can be detected and transmitted to a corresponding evaluation circuit, by corresponding adjustment of the circuit. In practice, however, the design of the known vacuum switch is such that three electric contacts can be made, in response to different negative pressures, for controlling the motor speed by corresponding switching actions. This is achieved by a contact plate which is driven by a diaphragm and which coacts with counter-contact pieces which are arranged at different spacings relative to the contact plate and which are contacted successively by the contact plate, depending on the prevailing negative pressure. To establish the contact, the contact plate performs a pivoting movement. The different spacings can be adjusted by axial displacement of the counter-contact pieces.
The different contacts established permit, for example, the activation of (additional) resistors in the triggering circuit for a phase control controlling the drive motor of the blower of the vacuum cleaner. Consequently, it is possible to predetermine a number of different power stages for the blower drive motor equal to the number of contacts that can be made by the existing vacuum switches at different negative pressures of the vacuum cleaner. However, from the point of view of precision mechanics, the input required for the individual adjustments of the vacuum switch or vacuum switches responding to the respective negative pressures is quite considerable and is even increased by the additional setting work which is required subsequently.
According to another known system, there is provided a control switch which is automatically adjusted by the negative pressure generated by the blower of the vacuum cleaner and which either triggers different winding portions of the electric motor driving the blower or switches on or off corresponding series resistors in response to the prevailing negative pressure (DE-PS 573 224).
As the vacuum cleaner using this known control circuit is of the so-called beater-sweeper type where the front portion of the cleaner housing forms the suction nozzle over its whole width and accommodates an additionally driven beater roller, the control switch is designed in such a manner that it comprises a flap or plate which extends over the full width of the vacuum cleaner and is seated in the upper portion of the nozzle and which can be rotated, by the negative pressure prevailing at any time, about a pivot point so as to turn a wiper of the control switch via a linkage in such a way as to enable the switching actions between the windings or resistors. In order to permit the control flap to react to varying negative pressures, seals in the form of bellows are provided on both sides of the flap. It may be regarded as a disadvantage of such known control switches that the dimensions, in any case the width, of the pressure-sensitive area is practically as big as the vacuum cleaner housing and that the switching actions required for controlling the suction power can be effected only by applying considerable force, via a mechanical linkage, whose kinematic end portion is provided with a spring-loaded quick-break switch which is then immediately transferred to another switching state. The known device cannot react with the required sensitivity to minor differences in negative pressure, and in addition there is always the possibility that the whole automatic control system may quickly become unserviceable because it is arranged directly in the suction area and, consequently, exposed to the dirt particles which tend to settle everywhere and which may then present a considerable obstacle to, or may even fully suppress, the sliding movements required for the switching actions.
DE-OS 28 19 193 describes a vacuum cleaner equipped with a speed governor for the blower unit where a final control element of the control circuit of the blower motor reacts to the negative pressure generated by the blower in operation. The final control element comprises an intake piston seated in a cylindrical housing which communicates with a vacuum connection, and the piston rod of the intake piston is coupled with a slide resistance which in turn is part of the automatic control system for the motor. Although this arrangement provides an analogue possibility to influence the blower motor control, it also requires that considerable negative pressures be made available for rendering possible the control movements of the piston in its cylinder, which are heavily impaired by friction, and the sliding movements of the slide resistance. However, the variations in negative pressure encountered in vacuum cleaners, for example in response to the filling level of the dust bag, are in some cases extremely small so that they cannot be utilized for controlling the blower motor.
DE-GM 80 00 772 proposes to influence the control of the suction power of an electric vacuum cleaner manually either by providing a plurality of vacuum switches having different switching thresholds so that the motor power can be subdivided into additional power stages, or by providing additional switching positions for an existing vacuum switch. The publication does, however, not provide any information as to how this can be achieved. It is particularly problematic in this case that when a plurality of vacuum switches is arranged the switch having the highest sensitivity value necessarily has to take part in all switching actions so that it is not possible, at least not in the manner described in such general terms, to effect specific switching actions at different negative-pressure values. In addition, it may be a disadvantage that the at least one vacuum switch provided must present an extreme hysteretic behavior if after switching over to another switching state, for example as a result of a variation in negative pressure provoked manually, for example by blocking the suction line, it is to remain in this state even when the suction line is released later. On the other hand, however, the publication also states that the system will switch back to its original state after full release of the suction line.
Another manual suction power control for a vacuum cleaner has been known from DE-PS 33 07 002. Here, too, at least two diaphragm switches which are set to different response thresholds, i.e. sensitivity values, are arranged in the negative pressure area of the vacuum cleaner. The design of the diaphragm switches is such that they respond to variations in negative pressure provoked deliberately by blocking manually the suction line whereby a subsequent speed control circuit is enabled to switch over between three power stages, for example. However, it is a problem of this known manual suction power control that the vacuum switches will of course also respond to pressure peaks occurring unintentionally in operation or to general pressure variations, and that above all the individual diaphragm switches will have to be interlocked mutually since otherwise all vacuum switches, including those which are set to lower vacuum threshold values, will respond simultaneously if a sufficiently strong pressure variation is encountered.
Now, it is the object of the present invention to designate automatic control device for the suction power of a vacuum cleaner in such a manner that the power control obtained operates sensitively, i.e. practically in imperceptible steps, that the design is such that frequent switching, i.e. frequent variations of the power data of the blower drive motor of the vacuum cleaner are avoided, and that the control arrangement exhibits a simple, reliable and particularly low-cost structure, also from the point of view of precision mechanics.
The invention solves this problem with the aid of the characterizing features of the main claim and provides the decisive advantage that the only two vacuum switches required provide a window effect for the pressure conditions which can be evaluated electronically so that it is now possible, on the one hand, to utilize the full power range of the blower drive motor for the vacuum cleaner and, on the other hand, to achieve long-term plateau operation for the drive motor so that excessively frequent switching is avoided while on the other hand any switching operation that may become necessary due to changed external operating conditions will be effected sensitively and without reving up the motor abruptly. It is ensured in this case that the predetermined power value of the blower drive motor will be maintained, i.e. that no switching will take place, as long as the vacuum values, for example in the suction area of the vacuum cleaner, remain within a defined vacuum window. As soon as the desired vacuum value can no longer be kept within this defined window, the two pressure switches determining an upper and a lower pressure threshold value, respectively, will react by a corresponding adjustment of the power of the drive motor, which is achieved by their combined effect, so that the vacuum value will be returned to within the range defined by the window.
It has become possible in this manner to prevent the power control of the blower drive motor from oscillating and, under certain circumstances, to operate the vacuum cleaner, even for extended times, at a constant power level exactly adapted to the respective operating requirements. The input circuit for the control circuit, which determines the power output of the blower drive motor, is provided with a memory function so that previous operating conditions and the vacuum data that can be derived therefrom are also taken into consideration for determining the momentary power output of the vacuum cleaner. Consequently, the invention is no regulating switch of the usual type which evaluates comparisons between a desired value and an actual value and which then tries to remove any deviation resulting therefrom. In contrast the deviation which is derived from the comparison between the desired value and the actual value and which is represented, in the case of the invention, by a specific switching contact combination of the two vacuum switches, is at first processed, giving due consideration to previous switching conditions and certain related, stored values, and is then used for deriving therefrom the triggering value for the motor power switching circuit.
According to a first embodiment of the invention, the structure of such a control circuit is simplified advantageously by the fact that apart from the two vacuum switches which are set to different pressure values the arrangement only includes a counter, a timer, a decoder connected to the output of the counter, and a phase control for the power control of the motor which is triggered by the decoder. The individual components may all be highly integrated, or else the entire circuit may be integrated and mounted, together with the two vacuum switches, on one circuit board or card, or stored as a program sequence in a computer or microprocessor processor--this applies to both embodiments.
According to another embodiment of the invention, an analogue storage, in the simplest of all cases a capacitor, is provided instead of a counter operating as a storage or memory, in which case the charging condition of the analogue storage, which is a function of the switching configuration of the two vacuum switches, determines the power output of the vacuum cleaner in automatic operation. It goes without saying that there are further provided additional conventional switching-over means which can be used by the operator for switching off the automatic feature and switching over to specific power stages manually, for example to a maximum or a minimum power stage.
Depending on the type of the recorded negative pressures acting on the pressure switches, it is finally possible to tailor the control circuit for the blower motor to specific operating requirements, giving regard either predominantly to the properties of the floor on which the vacuum cleaner is to be operated, or--alternatively or in addition--to the filling level of the dust bag. This can be achieved by detecting the prevailing negative pressure, which is supplied to the vacuum switches, in different areas of the vacuum cleaner, for example in the nozzle intake area or, in the case of a cylinder cleaner, for example at the point where the pipe opens into the main body of the vacuum cleaner, or in the area behind the dust bag and before the blower, or by detecting the pressure of the exhaust flow behind the blower. These conditions depend of course also on the particular arrangement of the individual components in the vacuum cleaner; in certain types of vacuum cleaner the dust bag may of course also be arranged behind the blower.
It is not necessary to arrange the vacuum switches at the described points physically; rather, it will be sufficient for the purposes of the invention if the vacuum is tapped at those points by means of small connection hoses and supplied, via small hoses, to the respective surfaces of the pressure switches which as such may be arranged at a different point, or may even be enclosed in a separate, small protective housing.
The features described by the sub-claims permit certain advantageous improvements and developments of the device specified by the main claim. A particularly advantageous solution is seen in the use of pneumatic diaphragm switches as pressure switches, as certain special embodiments thereof can be adjusted to the respective desired vacuum threshold values very sensitively. Certain known embodiments of such vacuum switches, which are preferably diaphragm-controlled, are described in detail by the before-mentioned DE-PS 31 17 507 and DE-PS 33 07 002 of the same applicant. In this connection, vacuum diaphragm switches are preferred which are capable of performing several switching operations in one housing, for example due to the possibility to pivot a diaphragm-driven contact plate. Consequently, it is also possible to use a single diaphragm switch comprising several adjustable switching positions, for example one of the type described by DE-PS 31 17 507, and to leave one of the existing three switching contacts unused as only two switches are required for the purposes of the present invention.
It is further regarded as advantageous if the counter according to the first embodiment of the invention, whose output configuration--which may be supplied for example in the form of a BDC code--controls the respective power stages of the blower motor, is provided with interlocking and reset means in such a manner that the counter will not flow over (revert to the lowest count) when being activated continuously, but will be kept at, or set back to final values in this case so as to prevent abrupt transitions and variations in the control of the blower motor.
It is further regarded as advantageous if a luminous band or strip, which may also consist of discrete individual lamps, can be activated in such a manner as to provide the operator with information as to which of the suction power stages available is switched on at any time. Generally, the adaptation to changing conditions works automatically, but given the plurality of possible switching stages it is also possible to predetermine certain particularly advantageous regulating characteristics for the speed of the blower motor of the vacuum cleaner. So, it is possible for example to increase or reduce the speed and, correspondingly, the suction power made available as the negative pressure rises in the suction area; for example, when the suction brush is pressed more strongly upon the surface to be worked, for example the carpet or upholstery, or the like, and is thus blocked, the suction power available may also be increased so that greater dirt particles, lint or threads can be picked up by the vacuum cleaner under difficult conditions. Finally, the arrangement may be further supplemented by manual change-over means, which may be arranged for example in the area of the operating handle and which may consist of switches by which certain basic values or selective operating behavior patterns can be preselected externally for the control and regulating circuit for the cleaning power so that the vacuum cleaner can then be operated in the manner of different cleaning programs. So, it is possible for example, when cleaning curtains or other light material, to limit the maximum suction power by blocking for example certain counter positions. However, it should be noted in this connection that basically the automatic power control according to this invention is a regulating process which consists in tapping the vacuum produced by the blower motor in the form of an actual value, comparing the latter with corresponding threshold values (for example in the manner of a window discriminator) and adjusting the control of the blower motor correspondingly.